Overheads

For calculation of specific system overheads where these are critical to your observing program (for example time-resolved observations), the detailed information on this page may be used. The detailed overhead information is also useful for the Phase II planning of your observing program. The various overheads can be broken into the following categories:

Telescope setup (acquisition) time

The setup times below include slewing to a new target, starting guiding, and accurately centering objects on slits (if appropriate).

FLAMINGOS-2 mode

Config Time

Imaging

15 minutes

Long slit Observations

20 minutes

MOS Obsevations

35 minutes

Applicants for FLAMINGOS-2 time should allow for one acquisition for approximately every 2 hours observed (including overheads and calibrations). Shorter observations may also be split in
order to accommodate them in the queue planning.

FLAMINGOS-2 configuration times

Below are listed approximate configuration times for various components within FLAMINGOS-2 (the exact times depend on the details of the positions between which a particular component is being moved). It is possible to reconfigure FLAMINGOS-2 while slewing to a new target, but it is not currently possible to reconfigure FLAMINGOS-2 while reading out the detector. This is a limitation of the current software that is used to execute sequences.

FLAMINGOS-2 component

Config Time

Filter change

~50 sec

Grating change

~40 sec

Mask move in or out

~100 sec

Readout times

Below are listed the overheads associated with reading out the array for both readmodes: a single CDS pair and for the correlated multiple sample (CMS) mode. The total readout time for the multi-read mode depends upon the number of reads (nreads); thus for 8 reads, the readout overhead is 20 sec.
At present it is not possible to reconfigure FLAMINGOS-2, dither the telescope position or begin setup on the next target during readout.

Read Mode

Time

CDS pair

8 sec

CMS reads

8 + (nreads*1.5) sec

Telescope offsetting time

The time to offset the telescope as part of a dither sequence is currently approximately 5-10s (from the time of turning off guiding at one position to guiding at the next position). At present it is not possible to offset the telescope while reading out the detector when these operations are part of a sequence.

Configuration for Calibrations

A portion of the overhead for taking calibrations is the time it takes to move the science fold mirror, which sends the beam either from the sky or from GCAL into FLAMINGOS-2. Again, when using the sequence executor to run sequences, this move cannot be done while reading out the detector array.

With FLAMINGOS-2 on side port 5, the relevant science fold moves take about 30 seconds each.